(at around 1h 5 mins) The porn film the guard at the factory watches on the DVD player is Sex Fever (2003), the X-rated parody of Roth's first film Cabin Fever (2002).
Eli Roth initially wanted to do a documentary on the subject of the "murder vacation". However, as he was doing research, he found it almost impossible to get into contact with people involved in such business, and that he could put himself in danger for asking around. He decided to use the subject for a fiction, instead. In 2022 though, a documentary maker, Miran Zupanic, of another ex-Yugoslavian state (to the one this film set in) did so reference such tourism murder in his 'Sarajevo Safari', when on 'sniper tourism' alleged to have occurred by such rich individuals bought opportunity to snipe at residents of besieged Bosnian capital city of Sarajevo, in the Serb-Bosnian conflict of '92.
The interior of the slaughterhouse was filmed at a functioning mental hospital in Prague built in 1910, in a wing that had been closed for over 50 years. Building 10, where many of the scenes were filmed, was where the craziest patients were taken. The basement was so creepy that Eli Roth had a string quartet playing classical music to make it feel cozier while shooting.
Over 150 gallons of blood were used in the making of the film, nearly three times the amount used on Eli Roth's first film Cabin Fever (2002).
Milda Jedi Havlas: the film's production assistant can be seen as the male desk clerk at the Slovakian hostel. He played the part to replace an actor who dropped out shortly before his scenes were to be filmed.
Eli Roth: (at around 3 mins) the American customer in a Boston Red Sox jersey in the Amsterdam coffee shop laughing at his friend struggling to take a hit off of a bong.
Eli Roth: [youthful and culture clash] The kids in Cabin Fever (2002) and both Hostel films leave their home environments to go somewhere they can behave irresponsibly and with no repercussions. This behavior ultimately leads to their demise. Another trademark of Roth's is culture clash. In Cabin Fever, it's suburban vs. rural, while in the Hostel films, it's West and East. Similar elements are also used in Roth's The Green Inferno.